While it is well known that hormones and hormone-like growth factors are regulators of erythropoiesis, the mechanisms by which such regulation occurs are poorly defined. This has been due in part to the use of biochemically complex culture mixtures required for erythroid colony assays that may mask gtowth promoting or inhibiting effects. We have recently developed a hormone-depleted culture system to measure the effects of hormones and soluble and insoluble erythroid growth factors that we have detected in cell conditioned medium. The focus of this proposal is to utilize such a system to: 1. Examine interactions of hormones with other growth factors. Our goal is to characterize hormonal interactions and to define hormone requirements for the production and/or action of erythroid growth promoting molecules. Factor deprivation experiments, dose-response curves, and stimulatory activity present in media conditioned by cell pulse-exposed to hormones will be analyzed. Soluble, hormone-induced stimulatory molecules will be characterized in relation to other growth factors and where appropriate purified by a variety of methods including column chromatography and lectin and immunoaffinity chromatography. In addition, we will determine whether hormones induce the release of insoluble growth factors from mononuclear cell surfaces. 2. Identify target cells of hormones and hormone-induced growth factors. We will define target cells of hormones and other growth factors by assaying such regulators in cultures depleted of specific mononuclear cell types based upon their surface characteristics. We will then add back these cells and determine whether their presence is critical for hormone action. 3. Correlate clinical and in vitro hormone responses. Studies of marrow cells from patients with deranged red cell production and from animals with experimentally-induced endocrine deficiency will explore the hypothesis that in an appropriate culture milieu in vitro cellular responses may reflect in vivo hormone responsiveness. They address the more general goal of this proposal which is to design new strategies for the therapy of anemias of varying etiologies.